1. Field of the Invention
This invention relates to an alkaline storage cell using hydrogen-storing alloy for the negative electrode.
2. Description of the Related Art
There is a great demand for the alkaline storage cell using hydrogen-storing alloy for the negative electrode, for consumer use, because of its characteristics such that it has a high capacity and that it is cleaner than the cells using lead or cadmium.
Specifically, for this type of alkaline storage cell, AB5-type rare-earth alloy such as LaNi5 is generally used. However, the discharge capacity of the cell using this type of alloy already exceeds 80% of the theoretical capacity, so that the possibility of further enhancing the capacity is limited. Meanwhile, the rare earth-Mg—Ni hydrogen-storing alloy obtained by replacing the rare-earth element in the AB5-type rare-earth alloy partly with Mg has a characteristic that it can store a larger amount of hydrogen gas than the AB5-type rare-earth alloy at temperatures close to room temperature. Hence, as disclosed in Japanese Unexamined Patent Publication No. 2000-73132, the development of the alkaline storage cell using the rare-earth magnesium alloy has been being advanced.
The alkaline storage cell using the rare earth-Mg—Ni hydrogen-storing alloy disclosed in the above-mentioned publication has, however, a problem that decrease in operating voltage due to repetition of a charge/discharge cycle occurs earlier, compared with the alkaline storage cell using the AB5-type rare-earth alloy.